1. Field of the Invention
The present invention relates to a vehicle battery system used for a vehicle having an electric drive such as an electric vehicle, a hybrid vehicle, and an electric train, or a general industrial power supply system. In addition, the present invention relates to a circuit board and an integrated circuit for these systems.
2. Description of Related Art
As Japanese Laid Open Patent Publication No. 2003-70179 discloses, a conventional battery system includes a battery module constituted by connecting a plurality of battery groups which are constituted by serially connecting a plurality of battery cells, and subordinate control devices that individually monitor the state of the battery cells for each of the battery groups. These subordinate control devices each receive a command from a higher-order control device through a signal transmission path. The signal transmission path is provided with an insulating circuit such as a photocoupler in order not to be influenced by a potential difference between the subordinate control device and the superior control device.
Since a vehicle body of an automobile, an electric train, or the like is easily contacted by a human body, it is necessary to improve safety. Therefore, a conventional battery system as described above mounted on a vehicle assumes a structure in which the battery system is electrically insulated from the vehicle body. The same is true for an industrial machine, i.e., the machine itself or the housing of the industrial machine is also easily contacted by a human body. Therefore, an electric power system of a conventional battery system as described above used for an industrial purpose is electrically insulated from the machine itself or the housing of the industrial machine so as to improve safety for a human body. On the other hand, since another electric power system with low source voltage such as a power source for control circuit does not negatively affect on a human body, a vehicle body or a housing may be used as a reference potential. In other words, a vehicle body or a housing may be used as a part of a low electric power system. In particular, a vehicle body is used as a part of a low electric power system for an automobile.
As described above, a conventional battery system is insulated from another electric power system so as to increase safety. In addition, in view of overhaul and repair of the system or the case of traffic accident, it is preferable for a battery system to be connected in series via an openable and closable connector. This structure opens the connector so as to cut off a DC supply current from the battery system, thereby improving safety.
A battery system with the structure as described above includes a plurality of serially connected battery cells that are further connected in series via the connector. In addition, the battery system with the structure as described above includes a plurality of integrated circuits that serve as battery cell controllers for measurement of terminal voltage at each battery cell, diagnosis for each battery cell, control of the state of charge of each battery cell, and the like (these functions are hereinafter collectively called battery cell processing). The plurality of integrated circuits that process the plurality of battery cells each include transmission circuits. The transmission circuits that each of the integrated circuits includes are also serially connected to each other, so that the serially connected transmission circuits form transmission paths.
The integrated circuits explained above are each electrically connected to the battery cells which are connected in series, and influenced by potentials of the connected battery cells. It is difficult to increase withstand voltage in these integrated circuits. If a high voltage is applied to the integrated circuits for some reasons, it exceeds the withstand voltage of the integrated circuits and they may be damaged. For example, when the connector that is serially connected to the battery cells is opened, the battery cells at the both ends of the connector are insulated from each other and therefore the potential state of the battery cells changes and a voltage exceeding the withstand voltage may be applied to some of the integrated circuits. Consequently, a highly reliable battery system that is less subject to change of the potential state of the battery cells caused by open/close of the connector is desired.